The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly includes at least one head, typically several, for reading and writing data from and to the disk. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The head stack assembly includes an actuator assembly, and at least one head gimbal assembly with a flexure. A conventional “rotary” or “swing-type” actuator assembly typically includes a rotary actuator having an actuator body. The actuator body has a pivot bearing cartridge to facilitate rotational movement of the actuator assembly. An actuator coil is supported by the actuator body and is configured to interact with one or more magnets, typically a pair, to form a voice coil motor. One or more actuator arms extend from an opposite side of the actuator body. This configuration of an actuator body and actuator arms is sometimes referred to as an “E-block.”
Each head gimbal assembly is attached to a distal end of one of the actuator arms. A head gimbal assembly includes a suspension assembly that supports a head. The suspension assembly includes a swage plate that is swage attached to the distal end of the actuator arm. The suspension assembly further includes a load beam and a hinge plate that is disposed between the swage plate and the load beam. Where the hinge plate is integrated with the load beam, the hinge plate may be referred to as a bend area of the load beam. The load beam is attached to the hinge plate with the load beam extending distally from the hinge plate and the actuator arm. The hinge plate allows the load beam to move the attached head relative to the actuator arm. The hinge plate may be formed to provide a pre-load of the load beam towards the disk. This pre-load allows the load beam to maintain the head at a desired fly height over the disk surface even while the disk and/or the actuator arm is vibrating.
The spindle motor typically includes a rotatable spindle motor hub, a magnet attached to the spindle motor hub, and a stator. The stator typically includes a series of coils that are in electrical communication with the printed circuit board assembly. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby imparting a rotational motion onto the spindle motor hub. Rotation of the spindle motor hub results in the rotation of the attached disks about a disk axis of rotation.
Disk flutter refers to one or more disk modes of vibration, wherein as the disk vibrates, the disk surfaces move up and down (i.e., along the disk axis of rotation). As the disk moves up, the top surface is in compression and the bottom surface is in tension. As the disk moves down, the top surface is in tension and the bottom surface is in compression. At least this tension and compression modality results in the tracks on the disk surfaces to have a motion that includes not only a component that is parallel to the disk axis of rotation, but also a component that is radial. Therefore, as the disk vibrates out of plane, the head assigned to follow a track upon the disk surface tends to become off-track. Specifically, as the disk moves up towards a head assigned to follow a track, such head tends to become off-track to the OD of the disk. As the disk moves away from a head assigned to follow a track, such head tends to become off-track to the ID of the disk.
During operation of the disk drive, the heads must be controllably positioned in relation to tracks of the disks. An approach to compensate for the disk flutter induced off-track motion is to vertically offset one side of the hinge plate of the suspension assembly relative to the associated actuator arm. The hinge plate may be attached to the actuator arm such that a side of the load beam that is closer to the disk axis of rotation is spaced closer to the disk surface than the other side of the hinge plate. This may be accomplished via a small spacer used to off-set one side of the hinge plate. With a side of the hinge plate off-set in this manner, flexing of the hinge plate to allow the head to move up and down also causes a compensatory radial motion of the head with respect to the disk. While such an offset hinge plate approach is effective in compensating for disk flutter induced off-track motion, this approach also introduces an additional and unintended source of (and sensitivity to) off-track motion when the actuator arm vibrates. Therefore, there is a need in the art to find a way to at least partially avoid or reduce an increase in off-track motion due to actuator arm vibration, while employing an offset hinge in the suspension assembly to reduce off-track motion due to disk vibration.